The present invention relates to fluid-actuated pumps in general, and more particularly to pneumatically actuated hydraulic pumps.
There is already known a variety of different pneumatically actuated pumps, such as hydraulic pumps, either of the single acting or of the double acting type. In such pumps there are usually provided interconnected reciprocating actuating and pumping pistons both being accommodated in their own chambers and the actuating piston having a larger active area than the pumping piston. The reciprocation of the actuating piston is controlled by a control valve which has a plurality of circumferential lands that separate individual connecting compartments from one another and also from control compartments provided at the one or the other end face of the control valve. Depending on the position of the control valve, one or both of the actuating compartments located to the two sides of the actuating piston are alternatingly supplied with pressurized fluid, or relieved of pressure, in that one of the connecting compartments permanently communicates with a source of a pressurized actuating fluid, while the other connecting compartment is permanently maintained at an atmospheric pressure. In this context, it is also already known to employ an auxiliary control valve which permanently communicates with the source of the pressurized actuating fluid and which has a displacing portion which extends into one of the actuating compartments and into the path of movement of the actuating piston to be displaced by the latter.
The heretofore known constructions of hydraulic pumps of this type are very complicated with respect to the pneumatically actuated part and the associated control arrangement and, therefore, such constructions are prone to malfunction. The control valve is relatively long and is provided, at the circumference thereof, with a plurality of mutually axially spaced lands equipped with sealing rings, as well as a plurality of annular compartments separated from one another by such lands. The control valve of the conventional construction is provided by an axial bore which extends over almost the entire length of the control valve, while two spaced radial bores each communicate the axial bore with one of the circumferential compartments. The axial bore serves solely the purpose of removal of expended air. The movement of the control valve by means of compressed air is achieved, on the one hand, by means of a peripheral annular surface and, on the other hand, by means of that end face of the control valve which is diametrally opposite to the port of the axial bore. Corresponding to the number of the circumferential annular compartments, there is needed a corresponding number of bores or annular grooves in the housing of the control valve. As a result of this, the control arrangement is very complicated and expensive, which has the disadvantageous effect of making the dimensions of the hydraulic pump with the associated equipment large and thus limiting the utility of the hydraulic pump to only some applications. A further disadvantage is to be seen in the fact that a separate and differently configurated control arrangement must be designed and manufactured, on the one hand, for a single acting pump and, on the other hand, for a double acting pump. As a result of this, the manufacture of the hydraulic pump is rendered more expensive and the keeping of the individual components in stock is rendered more difficult. In addition thereto, even the hydraulic part of the pump is complicated and, as a result of this, prone to malfunction, in that it usually consists of forged or wrought T-pieces or double-T-pieces with incorporated suction and pressure valves, which can only be manufactured with the necessary precision on special machines.